Memory system with block rearrangement to secure a free block based on read valid first and second data

ABSTRACT

A device includes a host including a main memory, and semiconductor memory including a nonvolatile semiconductor memory, memory unit, and controller. The nonvolatile semiconductor memory stores first address information. The memory unit stores second address information as part of the first address information. The controller accesses the nonvolatile semiconductor memory based on the second address information. Third address information is stored in the main memory, and is part or all of the first address information. The controller uses the third address information when accessing the nonvolatile semiconductor memory if address information to be referred is not stored in the second address information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims the benefitof priority under 35 U.S.C. § 120 from U.S. application Ser. No.15/833,336, filed Dec. 6, 2017, which is a continuation application ofand claims the benefit of priority under 35 U.S.C. § 120 from U.S.application Ser. No. 15/347,528, filed Nov. 9, 2016, which is acontinuation of U.S. application Ser. No. 14/965,545 filed Dec. 10,2015, now U.S. Pat. No. 9,542,117, which is a continuation applicationof U.S. application Ser. No. 13/561,392 filed Jul. 30, 2012, now U.S.Pat. No. 9,268,706, which is based upon and claims the benefit ofpriority under 35 U.S. § 119 from Japanese Patent Applications No.2011-168368, filed Aug. 1, 2011; and No. 2011-252001, filed Nov. 17,2011, the entire contents of all of which are incorporated herein byreference.

FIELD

Embodiments described herein relate generally to an informationprocessing device including a host device and semiconductor memorydevice, and to the semiconductor memory device.

BACKGROUND

A semiconductor memory device such as an SSD (Solid State Drive) oftenstores a logical-physical conversion table (MMU: to be also referred toas an L2P in some cases hereinafter) in, e.g., a buffer (memory) of theSSD. In this case, as a memory capacity of the SSD increases, a capacityand area of the buffer for storing the logical-physical conversion tabletend to increase. Also, a manufacturing cost often increases because itis necessary to secure the capacity for storing the logical-physicalconversion table in the buffer.

There is a technique called a UMA (Unified Memory Architecture). In theUMA, one memory is shared between a plurality of arithmetic processors.The UMA is used in a GPU (Graphical Processing Unit) or the like. Thearithmetic processors are integrated in the GPU. The UMA can reduce thememory cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of an informationprocessing device including a semiconductor memory device according to afirst embodiment;

FIG. 2 is an equivalent circuit diagram showing an example of a block ofa nonvolatile memory according to the first embodiment;

FIG. 3 is a flowchart showing an example of a boot operation accordingto the first embodiment;

FIG. 4 is a flowchart showing an example of a boot executing operationincluded in the boot operation according to the first embodiment;

FIG. 5 is a flowchart showing an example of a TLB operation according tothe first embodiment;

FIG. 6 is a flowchart showing an example of a DMA (Dynamic memoryaccess) operation according to the first embodiment;

FIG. 7 is a flowchart showing an example of a TLB operation according toa second embodiment;

FIG. 8 is a flowchart showing an example of a boot executing operationaccording to the second embodiment;

FIG. 9 is a block diagram showing an example of an arrangement of aninformation processing device according to a third embodiment;

FIG. 10 is a flowchart showing an example of an operation of theinformation processing device in a write process according to the thirdembodiment;

FIG. 11 is a flowchart showing an example of operations of asemiconductor memory device and the information processing device in thewrite process according to the third embodiment; and

FIG. 12 is a flowchart showing an example of operations of thesemiconductor memory device and the information processing device in aread process according to the third embodiment.

DETAILED DESCRIPTION

Each embodiment will be explained below with reference to theaccompanying drawings. Note that in the following explanation, the samereference numerals denote the same or almost the same functions andconstituent elements, and a repetitive explanation will be made asneeded.

First Embodiment

In general, according to a first embodiment, an information processingdevice includes a host device and a semiconductor memory device. Thehost device includes a main memory. The semiconductor memory deviceincludes a nonvolatile semiconductor memory, a memory unit, and acontroller. The nonvolatile semiconductor memory stores first addressconversion information and data. The memory unit stores second addressconversion information. The second address conversion information ispart of the first address conversion information. The controlleraccesses the nonvolatile semiconductor memory by referring to the secondaddress conversion information. Third address conversion information isstored in the main memory. The third address conversion information ispart of or all of the first address conversion information. Thecontroller uses the third address conversion information when accessingthe nonvolatile semiconductor memory if address conversion informationto be referred is not stored in the second address conversioninformation.

1. Configuration Example

1-1. Example of Overall Configuration

First, an example of an overall configuration of a memory systemincluding an SSD device according to the first embodiment will beexplained below with reference to FIG. 1.

As shown in FIG. 1, an information processing device according to thefirst embodiment includes an SSD (Solid State Drive) device 10 and hostdevice 20. The SSD device 10 is a device including a nonvolatile memoryto which the same interface as that of an HDD (Hard Disc Drive) isapplicable. A semiconductor memory device will be explained by takingthe SSD device 10 as an example in the first embodiment, but thesemiconductor memory device is not limited to the SSD device 10.Examples of the information processing devices are a personal computer,cell phone, and imaging device.

The SSD device 10 includes a nonvolatile memory (NVM) 11, TLB 14, buffermemory 15, ECC (Error Correcting Code) unit 16, bus master interface 17,DMA controller 18, and SSD controller 19. The nonvolatile memory 11stores an OS (Operating System) 12 and logical-physical conversion table(L2P) 13. The logical-physical conversion table 13 is used as addressconversion information.

For example, the host device 20 may an external device of the SSD device10.

In the first embodiment, a NAND type flash memory is applied as thenonvolatile memory (NVM) 11. Although details will be explained later,the NAND type flash memory includes a plurality of blocks, and data readand write are performed for each page unit. For example, the NAND typeflash memory includes a boot area 11-1 and a management area (or generalarea) 11-2 having a large capacity. Note that the nonvolatile memory 11is not limited to the NAND type flash memory, and may also be, e.g., anMRAM (Magnetoresistive Random Access Memory) or NOR type flash memory.

The boot area 11-1 starts from a fixed address and has a capacity ofabout a 1 Gigabyte unit. Also, the boot area 11-1 holds a boot programsimilar to a boot ROM/BIOS. The management area 11-2 is an area which nogeneral user can access, and the general area is an area which a generaluser can access.

The OS 12 is stored in the management area 11-2 of the NAND type flashmemory, and functions as a control program of the host device 20. The OS12 includes a driver for copying the logical-physical conversion table13 to a main memory 23, and driving the SSD device 10.

The logical-physical conversion table (L2P) 13 is information by which alogical block address (LBA) to be used when the external host device 20accesses the NAND type flash memory 11 is made to correspond to anactual physical block address (PBA) in the NAND type flash memory 11.

The logical block address (LBA) is a block address issued and managed bythe host device 20. The physical block address (PBA) is an actual blockaddress in the NAND type flash memory 11.

The TLB (Translation Look-aside Buffer) 14 is a buffer memory forcaching a part of the logical-physical conversion table 13.

The buffer memory 15 stores small-volume data of an input and output ofthe NAND type flash memory as the nonvolatile memory 11. The buffermemory 15 is, e.g., an SRAM (Static Random Access Memory) of about anorder of a few kB to a few hundred kB, and may also be a register or thelike. The buffer memory 15 can be omitted if the NAND type flash memory11 has an internal buffer memory.

The ECC unit 16 performs error check on readout data from thenonvolatile memory 11, and corrects an error if it is found.

The bus master interface 17 is a bus master of a bus (PCIe) 50 shown inFIG. 1, and includes the DMA controller 18.

The DMA controller 18 controls data transfer between the SSD device 10and the main memory 23 of the host device 20. The DMA controller 18 has,e.g., a function of sequentially transferring data of a plurality ofblocks to the host device 20 through the bus 50. In this embodiment, TheDMA controller 18 transfers address conversion information from the mainmemory of the host device 20 to TLB 14.

The SSD controller 19 controls the arrangement explained above, andcontrols an overall operation of the SSD device 10. In a read operation,the SSD controller 19 refers to the TLB 14 in accordance with a readcommand, converts a logical block address into a physical block address,and reads out data stored at this physical block address from thenonvolatile memory 11. In a write operation, the SSD controller 19refers to the TLB 14 in accordance with a write command, converts alogical block address into a physical block address, and writes data atthis physical block address of the nonvolatile memory 11.

The host device 20 includes a peripheral interface 21, a main memoryinterface 22, the main memory 23, and a processor 25.

The peripheral interface 21 is an interface with the SSD device 10 as aperipheral device, and functions as a bridge of the bus 50.

The main memory interface 22 is an interface of the main memory 23.

The main memory 23 is a main storage device for storing data of the hostdevice 20. In the first embodiment, a DRAM (Dynamic Random AccessMemory) or the like is used as the main memory 23. Also, the main memory23 according to the first embodiment stores a copy of (part of or allof) the logical-physical conversion table 13 described above. Details ofthe copy of the logical-physical conversion table 13 will be describedlater.

The processor 25 controls the arrangement explained above, and controlsthe operation of the host device 20. As the processor 25, it is possibleto use, e.g., a central processing unit (CPU), microprocessor unit(MPU), or digital signal processor (DSP).

In this embodiment, the SSD controller 19 accesses the nonvolatilememory 11 by using the copy of the logical-physical conversion table 13of the main memory 23 when accessing the nonvolatile memory 11 ifaddress conversion information to be referred is not stored in the TLB14.

1-2. Explanation of NAND Type Flash Memory

The nonvolatile memory 11 shown in FIG. 1 will be explained in moredetail below with reference to FIG. 2. The explanation will be made bytaking an equivalent circuit of block B1 including the NAND type flashmemory as an example. Since data is erased at once from memory cells inblock B1, the block B1 is a data erase unit.

Block B1 includes a plurality of memory cell units MU arranged in a wordline direction (WL direction). Each memory cell unit MU includes a NANDstring (memory cell string) including eight memory cells MC0 to MC7 thatare arranged in a bit line direction (BL direction) perpendicular to theword line direction and have current paths connected in series, asource-side selection transistor S1 connected to one end of the currentpath of the NAND string, and a drain-side selection transistor S2connected to the other end of the current path of the NAND string.

In the first embodiment, the memory cell unit MU includes the eightmemory cells MC0 to MC7. However, the memory cell unit MU need onlyinclude two or more memory cells, so the number of memory cells is notlimited to eight. For example, the number of memory cells in the memorycell unit MU may be 56, 32 or the like.

The other end of the current path of the source-side selectiontransistor S1 is connected to a source line SL. The other end of thecurrent path of the drain-side selection transistor S2 corresponds toeach memory cell unit MU, is formed above the memory cells MC0 to MC7 ineach memory cell unit MU, and is connected to a bit line BLm-1 extendingin the bit line direction.

Word lines WL0 to WL7 extend in the word line direction, and are eachconnected to control gate electrodes CG of a plurality of memory cellsin the word line direction. A selection gate line SGS extends in theword line direction, and is connected to a plurality of selectiontransistors S1 in the word line direction. A selection gate line SGDalso extends in the word line direction, and is connected to a pluralityof selection transistors S2 in the word line direction.

A page (PAGE) exists for each of the word lines WL0 to WL7. For example,page 7 (PAGE 7) exists for the word line WL7 as indicated by the brokenlines in FIG. 2. Since a data read operation and data write operationare performed for each page, the page is a data read unit and data writeunit.

2. Operation

2-1. Boot Process

The boot operation of the memory system including the SSD device 10according to the first embodiment will be explained below with referenceto a flowchart shown in FIG. 3. Note that in the following operation, astep represented by a parallelogram is executed through the bus 50.

First, in step S11 as shown in FIG. 3, the processor 25 of the hostdevice 20 reads out the boot program stored in the boot area 11-1 of thenonvolatile memory 11 of the SSD device 10.

Then, in step S12, the processor 25 executes boot by using the bootprogram read out from the boot area 11-1. Details of this boot executionwill be explained next with reference to FIG. 4.

Subsequently, in step S13, the processor 25 executes the loaded OS 12,and terminates the boot operation (End).

2-2. Boot Execution Process

Next, the boot executing operation of the memory system including theSSD device 10 according to the first embodiment will be explained withreference to a flowchart shown in FIG. 4. FIG. 4 corresponds to the bootexecution in step S12 of FIG. 3 described above.

First, in step S21 as shown in FIG. 4, the processor 25 of the hostdevice 20 makes a declaration of the use of the main memory 23, andsecures an area for storing a copy of the logical-physical conversiontable 13 in the main memory 23.

Then, in step S22, the processor 25 reads out the logical-physicalconversion table 13 stored in the nonvolatile memory 11, and stores, inthe secured area of the main memory 23, the copy of the logical-physicalconversion table 13 transferred through the bus 50. In the firstembodiment, an example in which the logical-physical conversion table 13is entirely copied to the main memory 23 will be explained. However,only a part of the logical-physical conversion table 13 may also becopied to the main memory 23. Details of this example in which only apart of the logical-physical conversion table 13 is copied to the mainmemory 23 will be explained in the second embodiment.

Subsequently, in step S23, the processor 25 similarly transfers andloads the OS 12 through the bus 50, and terminates this boot executionprocess (End).

2-3. TLB Process

The TLB operation of the memory system including the SSD device 10according to the first embodiment will be explained below with referenceto a flowchart shown in FIG. 5. The TLB operation uses the copy of thelogical-physical conversion table 13 transferred to the main memory 23of the host device 20 by the above-mentioned boot operation.

First, in step S31 as shown in FIG. 5, the SSD controller 19 of the SSDdevice 10 determines whether a corresponding logical address exists inthe TLB 14. If the corresponding logical address exists in the TLB 14and no TLB error occurs (No), the SSD controller 19 terminates theoperation (End).

On the other hand, if the corresponding logical address does not existin the TLB 14 and a TLB error occurs (Yes), the process advances to stepS32.

In step S32, the SSD controller 19 sets error information indicating theTLB error and a corresponding logical address.

In step S33, the SSD controller 19 transmits an interrupt to the hostdevice 20. After that, the SSD device 10 waits until the host device 20sends an instruction to activate the SSD device 10.

In step S34, the processor 25 of the host device 20 receives theinterrupt from the SSD device 10, and executes the following processing.

First, in step S35, the processor 25 acquires the set and transferrederror information and above-mentioned corresponding logical address.

Then, in step S36, the processor 25 refers to the copy of thelogical-physical conversion table 13 stored in the main memory 23.

Subsequently, in step S37, the processor 25 acquires a physical addresscorresponding to the logical address.

In step S38, the processor 25 transfers the acquired logical address andcorresponding physical address to the SSD device 10, and gives anactivation instruction to the SSD device 10 in the wait state.

In step S39, the SSD controller 19 of the SSD device 10 receives theactivation instruction from the host device 20, and starts activatingagain from the wait state.

In step S40, the SSD controller 19 selects an entry of the TLB 14 by LRU(Least Recently Used) or at random. LRU is to select an oldest accessedentry.

In step S41, the SSD controller 19 acquires the corresponding logicaladdress and physical address transferred from the host device 20.

In step S42, the SSD controller 19 sets (by replacement or copying) thelogical address and physical address in the entry of the TLB 14 selectedin step S40, and terminates the operation (End).

As described above, the SSD controller 19 executes an interrupt to thehost device 20 when address conversion information to be referred is notstored in the TLB 14 and acquires the address conversion information tobe referred from the copy of the logical-physical conversion table 13stored in the main memory 23 of the host device 20. Furthermore, the SSDcontroller 19 refers to address conversion information to be referredtransferred from the main memory 23 to the TLB 14 when the SSDcontroller 19 uses the copy of the logical-physical conversion table 13stored in the main memory 23 of the host device 20.

2-1. DMA Process

The DMA (Dynamic Memory Access) operation of the memory system includingthe SSD device 10 according to the first embodiment will be explainedbelow with reference to a flowchart shown in FIG. 6. This DMA operationis performed by using the copy of the logical-physical conversion table13 transferred to the host device 20 by the above-mentioned bootoperation, and corresponds to the above-mentioned TLB process.

First, in step S51 as shown in FIG. 6, the processor 25 of the hostdevice 20 refers to the copy of the logical-physical conversion table13, and sets a plurality of necessary logical addresses.

Then, in step S52, the processor 25 transfers the selected logicaladdresses, and gives an activation instruction to the SSD device 10.After that, the host device 20 waits until the SSD device 10 issues aninterrupt instruction.

Subsequently, in step S53, the SSD controller 19 of the SSD device 10receives the activation instruction from the host device 20, andactivates the SSD device 10.

In step S54, the SSD controller 19 acquires the transferred logicaladdresses.

In step S55, the SSD controller 19 refers to the logical-physicalconversion table 13 stored in the TLB 14, and sequentially transfers (byDMA) data stored at physical addresses corresponding to the logicaladdresses by using the bus master interface 17. This transfer mayinclude both read and write.

In step S56, the SSD controller 19 gives the host device 20 an interruptindicating the end of the transferred data.

In step S57, the processor 25 of the host device 20 receives theinterrupt, and starts the interrupt operation again from the wait state.

In step S58, the processor 25 uses the transferred data in a readoperation, or continues the processing in a write operation, andterminates the operation (End).

3. Effects

The semiconductor memory device and the system (information processingdevice) including the device according to the first embodiment achievesat least effects (1) and (2) below.

(1) A capacity and area of the buffer memory 15 of the SSD device 10 canbe reduced.

As described above, the SSD controller 19 of the SSD device 10 accordingto the first embodiment transfers a copy of the logical-physicalconversion table 13 to the host device 20 through the bus 50.

Subsequently, the processor 25 of the host device 20 makes a declarationof the use of the main memory 23, and secures an area for storing thecopy of the logical-physical conversion table 13 in the DRAM as the mainmemory 23 (S21). Then, the processor 25 stores the copy of thelogical-physical conversion table 13 transferred through the bus 50 inthe secured area of the main memory 23 (S22). After that, the processor25 loads the OS 12 as a control program of the host device 20, which istransferred through the bus 50, and terminates the boot executionprocess.

Consequently, the copy of the logical-physical conversion table 13 isplaced on the main memory 23 of the host device 20. This copy of thelogical-physical conversion table 13 stored in the main memory 23 of thehost device 20 is used as needed in the TLB operation shown in FIG. 5.For example, the copy of the logical-physical conversion table 13 storedin the main memory 23 is used as needed when, e.g., a correspondinglogical address does not exist in the TLB 14 and a TLB error occurs(Yes). In this case, it is unnecessary to refer to a main body of thelogical-physical conversion table (L2P) 13. This enables a high-speedoperation almost equal to that when a large amount of buffers are formedin the SSD device 10. In addition, since there is no large amount ofbuffers, the operation can be implemented with a very small amount ofhardware.

In the first embodiment, it is possible to reduce the capacity andoccupied area of the buffer memory 15 for storing the logical-physicalconversion table 13 of the SSD device 10.

Even in an arrangement in which the copy of the logical-physicalconversion table 13 is placed on the main memory 23 of the host device20, the SSD device 10 preferably includes high-speed processes such asTLB, DMA, and ECC in the first embodiment. The scale of the circuit forexecuting these processes is extremely smaller than that of a buffermemory for storing the whole logical-physical conversion table 13.

(2) The manufacturing cost can be reduced.

The manufacturing cost of the buffer memory 15 is higher than that ofthe DRAM as the main memory 23 of the host device 20.

In this embodiment as described above, the capacity and occupied area ofthe buffer 15 for storing the logical-physical conversion table 13 ofthe SSD device 10 are reduced, and a copy of the logical-physicalconversion table 13 is placed on the main memory 23 of the host device20. Therefore, the manufacturing cost can be reduced.

Second Embodiment

The second embodiment will now be explained. A memory system of thesecond embodiment has the same arrangement as that of the memory systemof the first embodiment shown in FIG. 1. In the first embodiment, themain memory 23 holds a copy of the logical-physical conversion table 13.The second embodiment differs from the first embodiment in that a mainmemory 23 holds a copy of a part of a logical-physical conversion table13. The second embodiment also differs from the first embodiment in aboot executing operation and TLB process as will be described later. Inthe following explanation of the second embodiment, a detailedexplanation of the same features as those of the first embodiment willbe omitted.

<TLB Process>

First, the TLB operation of the second embodiment will be explainedbelow with reference to FIG. 7.

The TLB operation of this embodiment differs from only step S36 of theTLB operation shown in FIG. 5 in the first embodiment. That is, in thefirst embodiment, no L2P error occurs in step S36 because the mainmemory 23 has a copy of the logical-physical conversion table (L2P) 13.In the second embodiment, however, an L2P error may occur in step S36because a copy of only a part of the L2P 13 is stored in the main memory23.

In the second embodiment, therefore, processing to be performed when anL2P error occurs is necessary, and the operation in step S36 is executedin accordance with a flowchart from (A) to (B) shown in FIG. 7.

First, in step S61 as shown in FIG. 7, a processor 25 of a host device20 determines whether address conversion information to be referred (acorresponding part of a logical-physical conversion table (L2P) 13)exists in the main memory 23. If the address conversion information tobe referred exists in the main memory 23 (Yes), the processor 25terminates this process (End).

If it is determined in step S61 that there is no address conversioninformation to be referred in the main memory 23 (No), the processor 25determines in step S62 whether there is a free space in the copy area ofthe main memory 23. If there is a free space in the copy area of themain memory 23 (Yes), the process advances to step S64.

If it is determined in step S62 that there is no free space in the copyarea of the main memory 23 (No), the process advances to step S63, andthe processor 25 selects an area of the main memory 23 in accordancewith the above-mentioned LRU, and empties the area.

Then, in step S64, the processor 25 acquires the address conversioninformation to be referred from the SSD device 10.

Subsequently, in step S65, the processor 25 sets the acquired addressconversion information to be referred in the free area formed in themain memory 23, and terminates the process (B).

In this embodiment as described above, the host device 20 acquiresaddress conversion information referred by the SSD controller 19 fromthe logical-physical conversion table 13 of the nonvolatile memory 11when the address conversion information referred by the SSD controller19 is not stored in the main memory 23.

<Boot Execution Process>

Next, the boot executing operation of the second embodiment will beexplained with reference to FIG. 8. The boot executing operation of thesecond embodiment differs from that of the first embodiment shown inFIG. 4 in that the L2P copy step (step 22 in FIG. 4) is omitted.

First, in step S71, the processor 25 of the host device 20 makes adeclaration of the use of the main memory 23, and secures an area forstoring a copy of the logical-physical conversion table 13 in the mainmemory 23.

Then, in step S72, the processor 25 loads an OS 12 transferred through abus 50. Since no copy of the logical-physical conversion table 13 isstored in the main memory 23, an L2P error occurs in the main memory 23.Even when an L2P error thus occurs in the boot operation, this L2P errorcan be eliminated by executing the process shown in FIG. 7 describedabove.

<Effects>

The semiconductor memory device and the system (information processingdevice) including the device according to the second embodiment achievesat least the effects (1) and (2) described previously. In addition, theabove-mentioned arrangements and operations can be applied as needed inthe second embodiment.

Third Embodiment

In general, according to a third embodiment, an information processingdevice includes a host device and a semiconductor memory device. Thehost device includes a main memory and a first controller. The firstcontroller separates a write request for the semiconductor memory deviceinto a write command and write data corresponding to the write command,outputs the write command to the semiconductor memory device, and storesthe write data in the main memory. The semiconductor memory deviceincludes a nonvolatile semiconductor memory and a second controller. Thesecond controller receives the write command transferred from the hostdevice, and, when executing the write command, acquires the write datacorresponding to the write command from the main memory, and writes thewrite data in the nonvolatile semiconductor memory.

FIG. 9 shows an example of an arrangement of an information processingdevice of the third embodiment. This information processing deviceincludes a host device (to be abbreviated as a host hereinafter) 30, anda memory system (semiconductor memory device) 40 that functions as astorage device of the host 30. The memory system 40 may also be anembedded flash memory complying with the eMMC (embedded Multi MediaCard) standards, or an SSD (Solid State Drive). The informationprocessing device may be, e.g., a personal computer, cell phone, orimaging device.

The memory system 40 includes a NAND flash 41 as a nonvolatilesemiconductor memory, a NAND interface 44, a DMA controller 45, a buffermemory 46, an ECC circuit 47, a storage controller 48, and a storageinterface 49.

The NAND flash 41 includes a memory cell array in which a plurality ofmemory cells are arranged in a matrix. Each memory cell can storemultilevel data by using a high-order page and low-order page. The NANDflash 41 is formed by arranging a plurality of blocks as data eraseunits. Each block includes a plurality of pages. Each page is a unit ofdata write and read. The NAND flash 41 is formed by, e.g., a pluralityof memory chips.

The NAND flash 41 stores user data transmitted from the host 30,management information of the memory system 40, and an OS 43 to be usedby the host 30.

The OS 43 functions as a control program of the host 30.

A logical-physical conversion table (L2P table) 42 is address conversioninformation by which a logical block address (LBA) to be used when thehost 30 accesses the memory system 40 is made to correspond to aphysical address (block address+page address+storage position in page)in the NAND flash 41. The L2P table 42 stored in the NAND flash 41 willbe called an L2P main body hereinafter.

The NAND interface 44 executes read/write of data and managementinformation on the NAND flash 41 based on a control of the storagecontroller 48.

The buffer memory 46 is used as a buffer for storing data to be writtenin the NAND flash 41, or data read out from the NAND flash 41. Thebuffer memory 46 also stores a command queue 46 a for queuing a commandfor a write request or read request input from the host 30, and taginformation 46 b of L2P information cached in a main memory 33 (to bedescribed later) of the host 30. The buffer memory 46 is formed by,e.g., an SRAM or DRAM, but may also be formed by a register or the like.

The ECC circuit 47 performs an encoding process of ECC processing (anerror correcting process) on data transferred from the buffer memory 46and scheduled to be written in the NAND flash 41, and outputs the datato the NAND interface 44 by adding the encoding result to the data.Also, the ECC circuit 47 performs a decoding process (an errorcorrecting process using an error correcting code) of ECC processing ondata read out from the NAND flash 41 via the NAND interface 44, andoutputs the error-corrected data to the buffer memory 46.

The DMA controller 45 controls data transfer between the NAND interface44, ECC circuit 47, and buffer memory 46. Note that the DMA controller45 may control data transmission between a register 34 a in a storageinterface 34 of the host 30 and the buffer memory 46, but the storageinterface 49 controls this data transmission between the register 34 aand buffer memory 46 in the third embodiment.

The storage interface 49 is an interface for connecting the memorysystem 40 and host 30. The storage interface 49 has a function ofcontrolling data transmission between the register 34 a in the storageinterface 34 of the host 30 and the buffer memory 46 of the memorysystem 40.

The function of the storage controller 48 is implemented by executingfirmware. The storage controller 48 comprehensively controls theconstituent elements in the memory system 40 connected to a bus 60.

In the memory system 40, the relationship between a logical address(LBA) and a physical address (a storage position in the NAND flash 41)is not statistically determined, but dynamically determined when writingdata. For example, the following processing is performed whenoverwriting data at the same LBA. Assume that valid block-size data isallocated to logical address A1, and block B1 of the NAND flash 41 isused as a memory area. When a command for overwriting block-size updatedata at logical address A1 is received from the host 30, an unused freeblock (block B2) in the NAND flash 41 is secured, and data received fromthe host 30 is written in the free block. After that, logical address A1and block B2 are associated with each other. Consequently, block B2becomes an active block including valid data. The data saved in block B1is invalidated, and block B1 becomes a free block.

In the memory system 40 as described above, even for data at the samelogical address A1, a block to be actually used as a recording areachanges whenever data is written. Note that when writing block-sizeupdate data, a write destination block always changes. However, whenwriting update data smaller than the block size, the update data may bewritten in the same block. For example, when updating page data smallerthan the block size, old page data at the same logical address isinvalidated and newly written latest page data is managed as a validpage in the same block. When all data in a block are invalidated, theblock is released as a free block.

Also, block rearrangement is executed in the memory system 40. If a dataerase unit (block) and data management unit are different in the memorysystem 40, invalid (non-latest) data makes holes in blocks as rewrite ofthe NAND flash 41 advances. If these blocks having holes increase,usable blocks practically reduce, and this makes it impossible toeffectively utilize the memory area of the NAND flash 41. Therefore, ifthe number of free blocks in the NAND flash 41 becomes smaller than apredetermined threshold value, block rearrangement such as compactionand garbage collection by which latest valid data are collected andrewritten in different blocks is executed, thereby securing free blocks.

Furthermore, when updating a partial sector in a page, the memory system40 executes read-modify-write (RMW) by which stored data in the NANDflash 41 is read out, changed, and rewritten in the NAND flash 41. Inthis RMW process, a page or block including a sector to be updated isfirst read out from the NAND flash 41, and the readout data isintegrated with write data received from the host 30. Then, theintegrated data is written in a new page or new block of the NAND flash41.

The host 30 includes a processor 31, a main memory interface 32, themain memory 33, the storage interface 34, and a bus 36 for connectingthese components. The main memory interface 32 is an interface forconnecting the main memory 33 to the bus 36.

The main memory 33 is a main storage device which the processor 31 candirectly access. In the third embodiment, a DRAM (Dynamic Random AccessMemory) is used. The main memory 33 functions as a main memory of theprocessor 31, and is used as a storage area for an L2P cache 33 a andwrite cache 33 b. The main memory 33 is also used as a work area 33 c.The L2P cache 33 a is a part or the whole of the L2P main body 42 storedin the NAND flash 41 of the memory system 40. The storage controller 48of the memory system 40 performs address resolution when accessing datastored in the NAND flash 41, by using the L2P cache 33 a cached in themain memory 33 and the L2P main body 42 stored in the NAND flash 41.

The write cache 33 b temporarily stores write data to be written in thememory system 40 from the host 30. The work area 33 c is used whenwriting data in the NAND flash 41. More specifically, the work area 33 cis used when executing the block rearrangement or RMW described above.

The storage interface 34 is an interface for connecting to the memorysystem 40. The storage interface 34 includes a DMA controller 35 and theregister 34 a. The DMA controller 35 controls data transfer between theregister 34 a in the storage interface 34, and the L2P cache 33 a, writecache 33 b and work area 33 c in the main memory 33.

The processor 31 controls the operation of the host 30, and executes theOS 43 loaded in the main memory 33 from the NAND flash 41. The OS 43includes a device driver 43 a for controlling the memory system 40. Whenaccepting a write request to the memory system 40 from the OS 43 or anapplication on the OS 43, the device driver 43 a separates the writerequest into a write command and write data. The command includes, e.g.,a field for identifying a command type (e.g., read or write), a fieldfor designating a start LBA, and a field for designating a data length.The device driver 43 a transmits the command to the memory system 40 viathe storage interface 34. On the other hand, the device driver 43 atemporarily stores the separated data in the write cache 33 b of themain memory 33.

FIG. 10 shows an example of an operation procedure of the device driver43 a when accepting a write request. When accepting a write request tothe memory system 40 from the OS 43 or an application on the OS 43, thedevice driver 43 a separates the write request into a command and data(step S100). Then, the device driver 43 a directly transmits the commandto the memory system 40 via the storage interface 34. Also, the devicedriver 43 a temporarily stores the separated data in the write cache 33b of the main memory 33 (step S110). This data cached in the write cache33 b is transferred to the memory system 40 after that based on acontrol of the storage controller 48 of the memory system 40.

FIG. 11 shows an example of an operation procedure of the memory system40 when a write command is received. The memory system 40 receives awrite command transmitted from the host 30 (step S200). The storageinterface 49 sets the received write command in the command queue 46 aof the buffer memory 46 (step S210). When the turn of execution of thewrite command set in the command queue 46 a comes and the write commandbecomes executable (step S220), the storage controller 48 determineswhether an LBA included in the write command is unwritten (step S230).“An LBA is unwritten” herein mentioned means a state in which valid datacorresponding to the LBA is not stored in the NAND flash 41.

More specifically, whether the LBA is unwritten is determined by, e.g.,the following procedure. That is, the storage controller 48 determineswhether the LBA included in the write command hits the tag information46 b. If the LBA does not hit, the storage controller 48 determineswhether the LBA hits the L2P main body 42 stored in the NAND flash 41.Note that the tag information 46 b is data in which the L2P informationcached in the L2P cache 33 b of the main memory 33 of the host 30 isregistered. Whether L2P information corresponding to the LBA is storedin the L2P cache 33 b can be determined by searching the tag information46 b.

If it is determined that the LBA does not hit by thus searching the taginformation 46 b and L2P main body 42 (Yes in step S230), the storagecontroller 48 outputs, to the DMA controller 35 of the host 30, a datatransfer command for transferring write data corresponding to the writecommand from the write cache 33 b (step S240). The DMA controller 35which received this data transfer command transfers write data stored inthe write cache 33 b of the main memory 33 to the register 34 a of thestorage interface 34 from the write cache 33 b of the main memory 33.When the data is set in the register 34 a, the storage interface 34notifies the storage interface 49 of the setting of the data, and thestorage interface 49 which received the notification transfers the writedata set in the register 34 a to the buffer memory 46 (step S250).

The write command may also include a storage position in the main memory33, so that the storage controller 48 can specify the storage positionof the write data stored in the write cache 33 b on the main memory 33.It is also possible to allow the storage controller 48 to specify thestorage position of the write data by giving the write cache 33 b anFIFO structure or ring buffer structure. That is, write data is set inthe write cache 33 b having the FIFO structure in the order of thegeneration of write commands. Since the write command includes the datalength, the storage controller 48 can grasp the storage position ofwrite data on the main memory 33 by adding the data length to an addresswhenever a write command is received, as long as the storage controller48 recognizes an initial address of the write cache 33 b having the FIFOstructure.

When the write data is set in the buffer memory 46 by the processing instep S250, the storage controller 48 causes the ECC circuit 47 toperform ECC encoding on the write data, and writes the encoded data in afree block of the NAND flash via the NAND interface 44 (step S350).After that, the L2P cache 33 a, tag information 46 b, and L2P main body42 are updated so that the LBA designated by the write commandcorresponds to the free block (step S360). Note that it is also possibleto periodically update the L2P main body 42, instead of updating the L2Pmain body 42 whenever data is written in the NAND flash 41.

The L2P cache 33 a is updated as follows. After forming new L2Pinformation on the buffer memory 46, the storage controller 48 adds taginformation of the new L2P information to the tag information 46 b ofthe buffer memory 46, and notifies the storage interface 49 of theaddition of the tag information. Also, the storage controller 48outputs, to the DMA controller 35 of the host 30, a transfer command fortransferring the L2P information. The storage interface 49 sets the newL2P information formed on the buffer memory 46 in the register 34 a ofthe storage interface 34. The DMA controller 35 transfers the L2Pinformation set in the register 34 a to the main memory 33, and cachesthe L2P information in the L2P cache 33 a.

On the other hand, if the LBA included in the write command hits the taginformation 46 b in step S230 (No in step S230), the storage controller48 outputs an L2P information transfer command to the DMA controller 35of the host 30. The DMA controller 35 transfers the hit L2P informationstored in the L2P cache 33 a of the main memory 33 from the main memory33 to the register 34 a of the storage interface 34. As describedpreviously, when the data is set in the register 34 a, the storageinterface 34 notifies the storage interface 49 of the setting of thedata, and the storage interface 49 which received this notificationtransfers the L2P information set in the register 34 a to the buffermemory 46. The storage controller 48 performs address resolution byusing the L2P information transferred to the buffer memory 46.

Then, the storage controller 48 reads out, from the NAND flash 41, apage or block including data stored in a physical address correspondingto the LBA obtained by the address resolution, and transfers the readoutpage or block to the buffer memory 46 (step S260). Subsequently, thestorage controller 48 outputs, to the DMA controller 35 of the host 30,a data transfer command for transferring the write data stored in thewrite cache 33 b (step S270). The DMA controller 35 which received thisdata transfer command transfers the write data stored in the write cache33 b of the main memory 33 from the main memory 33 to the register 34 aof the storage interface 34. The storage interface 49 transfers thisdata set in the register 34 a to the buffer memory 46 in the same manneras described above (step S280).

The storage controller 48 then composites, on the buffer memory 46, thedata read out from the NAND flash 41 and written in the buffer memory 46and the data transferred from the write cache 33 b and written in thebuffer memory 46 (step S290). When this composition is complete, thestorage controller 48 notifies the storage interface 49 of thecompletion of the composition, and outputs, to the DMA controller 35 ofthe host 30, a transfer command for transferring the data (step S300).The storage interface 49 sets the data composited on the buffer memory46 in the register 34 a of the storage interface 34. The DMA controller35 transfers the composited data set in the register 34 a to the mainmemory 33, and stores the composited data in the work area 33 c (stepS310).

After that, the storage controller 48 determines whether the datacomposition process is complete (step S320). If the data compositionprocess is not complete, the storage controller 48 repeats the procedurein steps S260 to S310 until the data composition process is complete,thereby forming as many block data as possible on the work area 33 c ofthe main memory 33.

When the data composition process is complete, the storage controller 48outputs, to the DMA controller 35 of the host 30, a data transfercommand for transferring the composited data stored in the work area 33c of the main memory 33 (step S330). The DMA controller 35 whichreceived this data transfer command transfers the composited data storedin the work area 33 c of the main memory 33 from the main memory 33 tothe register 34 a of the storage interface 34. The storage interface 49transfers this data set in the register 34 a to the buffer memory 46 inthe same way as described previously (step S340).

When the composited data is set in the buffer memory 46 by theprocessing in step S340, the storage controller 48 causes the ECCcircuit 47 to perform ECC encoding on the write data, and writes theencoded data in a free block of the NAND flash 41 via the NAND interface44 (step S350). After that, the storage controller 48 makes the LBAcorrespond to this free block, and updates the L2P cache 33 a, taginformation 46 b, and L2P main body 42 so as to invalidate the oldactive block (step S360).

Note that if the composition process is complete by performing datatransfer once from the main memory 33 to the buffer memory 46, the datacomposited on the buffer memory 46 may also be written directly in theNAND flash 41.

FIG. 12 shows an example of an operation procedure of the memory system40 when a read command is received. When the memory system 40 isreceived a read command via the storage interface 49, the storageinterface 49 sets the received read command in the command queue 46 a ofthe buffer memory 46 (step S400). When this read command becomesexecutable, the storage controller 48 searches the tag information 46 bfor an LBA included in the read command (step S410), and determineswhether the LBA included in the read command hits in the tag information46 b (step S420). If the LBA hits (Yes in step S420), the storagecontroller 48 outputs an L2P transfer command to the DMA controller 35of the host 30 (step S430). The DMA controller 35 transfers the hit L2Pinformation stored in the L2P cache 33 a of the main memory 33 from themain memory 33 to the register 34 a of the storage interface 34. Thestorage interface 49 transfers the L2P information set in the register34 a to the buffer memory 46 in the same manner as described earlier(step S440).

The storage controller 48 performs address resolution by using the L2Pinformation transferred to the buffer memory 46. That is, the storagecontroller 48 acquires a physical address corresponding to the LBA fromthe L2P information, and reads out data corresponding to the acquiredphysical address from the NAND flash 41. The ECC circuit 47 performs adecoding process of ECC processing on the data read out from the NANDflash 41 via the NAND interface 44, and outputs the error-corrected datato the buffer memory 46. After that, the storage controller 48 outputsthe readout data stored in the buffer memory 46 to the host 30.

On the other hand, if the LBA included in the read command does not hitthe tag information 46 b in step S420 (No in step S420), the storagecontroller 48 reads out part of or all of L2P main body stored in theNAND type flash memory 41 to the buffer memory 46, and executessearching (step S460). If the LBA does not hit the L2P main body, thestorage controller 48 terminates the read process, and returns an errorto the host 30. If the LBA hits the L2P main body (step S470), thestorage controller 48 performs address resolution by using the hit L2Pinformation. That is, the storage controller 48 acquires a physicaladdress corresponding to the LBA from the L2P information, and reads outdata corresponding to the acquired physical address from the NAND flash41. The ECC circuit 47 performs a decoding process of ECC processing onthe data read out from the NAND flash 41 via the NAND interface 44, andoutputs the error-corrected data to the buffer memory 46. After that,the storage controller 48 outputs the readout data stored in the buffermemory 46 to the host 30 (step S480).

The storage controller 48 commands the storage interface 49 to transfer,to the register 34 a of the storage interface 34, L2P informationcorresponding to the LBA included in the read command, or L2Pinformation corresponding to a peripheral LBA including the LBA includedin the read command, from the L2P main body 42 read out to the buffermemory 46. Also, the storage controller 48 outputs, to the DMAcontroller 35 of the host 30, a transfer command for transferring theL2P information. The storage interface 49 sets, in the register 34 a ofthe storage interface 34, the L2P information buffered in the buffermemory 46. The DMA controller 35 transfers the L2P information set inthe register 34 a to the main memory 33, and caches the L2P informationin the L2P cache. In response to this, the storage controller 48 updatesthe tab information 46 b of the buffer memory 46.

Note that the work area 33 c formed on the main memory 33 is also usedas a work area for performing, e.g., the block rearrangement and RMWdescribed previously. Note also that the memory system 40 has the taginformation 46 b of the L2P cache 33 a in the third embodiment, but thememory system 40 need not have the tag information 46 b and may directlysearch the L2P cache 33 a. Furthermore, the storage interface 49 of thememory system 40 performs data transfer between the register 34 a andbuffer memory 46 in the third embodiment, but the storage controller 48may perform this data transfer. It is also possible to perform datatransfer directly between the main memory 33 and buffer memory 46.

In the third embodiment as described above, the main memory 33 of thehost 30 is used as the storage area of the write cache 33 b and L2Pcache 33 a. Therefore, the memory capacity of the buffer memory 46 canbe reduced. In addition, in the third embodiment, a write command andwrite data are separated when write is requested, the write data isstored in the main memory 33 of the host 30, and the write command isstored in the buffer memory 46 of the memory system. When the memorysystem 40 executes the write command, the write data is read out fromthe main memory 33 of the host 30, and written in the NAND flash 41.When compared to an operation in which a write command and write dataare not separated, therefore, the interface band width between the host30 and memory system 40 can be reduced. That is, when a write commandand write data are not separated, the host transfers the write commandand write data to the memory system when write is requested. Then, thememory system separates the write command from write data, and transfersthe separated write data to the main memory 33 of the host 30. Whenexecuting the write command, the memory system reads out the write datafrom the main memory of the host, and writes the readout data in theNAND flash. In this operation, the write data is transferred through thebus between the host and memory system three times for one writerequest, and this increases the interface band width. By contrast, thearrangement of this embodiment can solve this problem.

Note that when activating the memory system 40, the L2P main body 42stored in the NAND flash 41 may also be loaded into the main memory 33of the host 30. Note also that it is possible to form a primary cache ofL2P information in the memory system 40, form a secondary cache of L2Pinformation in the main memory 33 of the host 30, and search the L2Pmain body 42 stored in the NAND flash 41 if there is no hit in theprimary and secondary caches.

Furthermore, in the third embodiment, the work area 33 c to be used bythe storage controller 48 of the memory system 40 is formed on the mainmemory 33. This makes it possible to reduce the capacity and occupiedarea of the buffer for the work area in the memory system 40.

In the third embodiment as explained above, the capacity of the buffermemory 46 of the main memory 40 can be reduced without increasing theinterface band width between the host 30 and memory system 40.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A memory system comprising: an interface circuitconfigured to communicate with a host device, the host device includinga first semiconductor memory; a second semiconductor memory including aplurality of blocks including a first block, a second block, and a thirdblock, each of the blocks being a unit of an erase operation of thesecond semiconductor memory, the second semiconductor memory beingnonvolatile; and a controller circuit configured to, in a case that ablock rearrangement to secure a free block is executed in the memorysystem, read a valid first data from the first block, write the readfirst data into an area of the first semiconductor memory of the hostdevice, the area having been designated by the host device for storingdata from the memory system, read a valid second data from the secondblock, write the read second data into the area of the firstsemiconductor memory, read the first data and the second data from thearea of the first semiconductor memory, and write the read first dataand the read second data into the third block.
 2. The memory systemaccording to claim 1, wherein the block rearrangement includes at leastone of: a compaction process, a garbage collection process, aread-modify-write (RMW) process.
 3. The memory system according to claim1, wherein the block rearrangement includes a read-modify-write (RMW)process, the controller circuit is configure to integrate the validfirst data and the valid second data with write data received from thehost device and write the valid first data and the valid second dataintegrated with the write data into the third block in the RMW process.4. The memory system according to claim 1, wherein the blockrearrangement is executed when a number of the free blocks becomessmaller than a threshold value.
 5. The memory system according to claim1, wherein the controller circuit is configure to use a work area of thefirst semiconductor memory when the controller circuit reads the firstdata and the second data from the area of the first semiconductor memoryand writes the read first data and the read second data into the thirdblock.
 6. The memory system according to claim 1, wherein the thirdblock is a free block.
 7. A storage system comprising: a host deviceincluding a first semiconductor memory; and a memory system configuredto communicate with the host device, the memory system comprising: asecond semiconductor memory including a plurality of blocks including afirst block, a second block and a third block, each of the blocks beinga unit of an erase operation of the second semiconductor memory, thesecond semiconductor memory being nonvolatile; and a controller circuitconfigured to, in a case that a block rearrangement to secure a freeblock is executed in the memory system, read a valid first data from thefirst block, write the read first data into an area of the firstsemiconductor memory of the host device, the area having been designatedby the host device for storing data from the memory system, read a validsecond data from the second block, write the read second data into thearea of the first semiconductor memory, read the first data and thesecond data from the area of the first semiconductor memory, and writethe read first data and the read second data into the third block. 8.The storage system according to claim 7, wherein the block rearrangementincludes at least one of: a compaction process, a garbage collectionprocess, a read-modify-write (RMW) process.
 9. The storage systemaccording to claim 7, wherein the block rearrangement includes aread-modify-write (RMW) process, the controller circuit is configure tointegrate the valid first data and the valid second data with write datareceived from the host device and write the valid first data and thevalid second data integrated with the write data into the third block inthe RMW process.
 10. The storage system according to claim 7, whereinthe block rearrangement is executed when a number of the free blocksbecomes smaller than a threshold value.
 11. The storage system accordingto claim 7, wherein the controller circuit is configure to use a workarea of the first semiconductor memory when the controller circuit readsthe first data and the second data from the area of the firstsemiconductor memory and writes the read first data and the read seconddata into the third block.
 12. The storage system according to claim 7,wherein the third block is a free block.
 13. The storage systemaccording to claim 7, wherein the host device further comprises a DMAcontroller configured to transfer the first data and the second datastored in the first semiconductor memory to the memory system.
 14. Amethod for a memory system capable of communicating with a host devicehaving a first semiconductor memory, the memory system including asecond semiconductor memory including a plurality of blocks including afirst block, a second block, and a third block, each of the blocks beinga unit of an erase operation of the second semiconductor memory, thesecond semiconductor memory being nonvolatile, the method comprising:executing a process of, in a case that a block rearrangement to secure afree block is executed in the memory system: reading a valid first datafrom the first block; writing the read first data into an area of thefirst semiconductor memory of the host device, the area having beendesignated by the host device for storing data from the memory system;reading a valid second data from the second block; writing the readsecond data into the area of the first semiconductor memory; reading thefirst data and the second data from the area of the first semiconductormemory; and writing the read first data and the read second data intothe third block.
 15. The method according to claim 14, wherein the blockrearrangement includes at least one of: a compaction process, a garbagecollection process, a read-modify-write (RMW) process.
 16. The methodaccording to claim 14, wherein the block rearrangement includes aread-modify-write (RMW) process, the method further comprising,integrating the valid first data and the valid second data with writedata received from the host device and writing the valid first data andthe valid second data integrated with the write data into the thirdblock in the RMW process.
 17. The method according to claim 14, whereinthe block rearrangement is executed when a number of the free blocksbecomes smaller than a threshold value.
 18. The method according toclaim 14, further comprising: using a work area of the firstsemiconductor memory when the controller circuit reads the first dataand the second data from the area of the first semiconductor memory andwrites the read first data and the read second data into the thirdblock.
 19. The method according to claim 14, wherein the third block isa free block.